1. Field of the Invention
The present invention relates to a method for controlling an image forming apparatus, and more particularly, to a method for controlling an image forming apparatus for forming a black and white image or a color image, which senses density of an image pattern formed on a photosensitive body or a transfer body by use of a density sensor, and controls an image forming condition according to the sensed result.
2. Description of the Related Art
An image forming apparatus generally prints either a black and white image or a color image, by scanning a light on a photosensitive body charged to a predetermined electric potential to form an electrostatic latent image, developing the electrostatic latent image using toner, and transferring and fusing the developed toner image onto paper.
In a case where an image forming apparatus is configured to print a color image, multiple color toners, typically, yellow (Y), magenta (M), cyan (C) and black (K) are used. That is, four developing devices may be needed for forming toner images of four colors. There are, broadly speaking, two types of color image forming apparatuses, one of which is a single pass type having four pairs of exposure units and photosensitive bodies, the single color toner image produced by each pair are overlapped with images of other pairs to produce the color image, while the other type being a multi-pass type which is provided with a single exposure unit and a single photosensitive body.
Several different types of developer are available for use in an image forming apparatus, including, for example, a wet type developer that includes powder type toner particles dispersed in a liquid type carrier, a dry type developer, including, e.g., two-component developer, in which non-magnetic toner particles are mixed with magnetic carriers, one component developer with either magnetic or non-magnetic toner particles, or the like.
In an image forming apparatus using dry type developer, e.g., two component developer, because the electrostatic latent image is developed by the use of only the toner particles, it may be of a particular importance to properly control the supply of the toner to maintain the toner density within an adequate range.
One control method conventionally used to control the toner density is to sense the toner density of an image pattern formed on a photosensitive medium or a transfer belt, and using the sensed toner density to control the supply of the toner. An example of such a conventional toner density control method is disclosed in Japanese Patent Laid-open Publication No. 2002-162795 to Makoto et al. (“Makoto”). According to the conventional toner density control method described by Makoto, a reference image pattern is first developed, and then density of the image pattern is sensed, and a determination is made as to whether the density of the image pattern is higher or lower than preset reference density. If it is determined that the density of the image pattern is lower than the preset reference density, additional toner is supplied to the developing unit.
However, in an image forming apparatus using dry type developer, e.g., two-component type developer, with the increased level of charge of the developer, a less amount of toner may be supplied to the photosensitive body. For this reason, even when a sufficient amount of toner exists in the developing unit, the amount of toner supplied to the photosensitive body may be lower than the reference value. In this situation, if the additional toner is supplied to the developing unit to adjust the density of the image pattern according to the conventional control method, an excessive toner supply may occur, in which the relative amount of toner without sufficiently charge becomes proportionally large, which in turn may result in toner scattering phenomenon and/or background contamination.